Update to engine problems, 96 SL500. Need input - PeachParts Mercedes-Benz Forum

spinedoc · #1 11-26-2007, 10:50 AM

Anyway to make a short story long, here's what happened:

Car was running perfectly, but had a very very small tick occasionally, my mechanic mentioned it, but we never took it any further for a couple of years. I change the oil every 7500 miles with Mobil 1 Synthetic.

The other week the car lost a ton of power and eventually left me stranded with cylinder misfire codes. We thought it was the MAF or a timing chain jump at first, but it ended up being the fuel pressure regulator, fixed it and the problems was fixed, but keep in mind that the oil got flooded with gas.

So now the car is back together, but it has a HUGE klacking. My mechanic first thought was a rod knock, we take it to a couple of engine guys and they listen around and say they can't tell without cracking it open, pretty inconclusive. We did check compression and it's very strong in all cylinders, my first impression was piston slap, but there is no oil consumption and good compression.

My mechanic is a personal friend, so he gets down to getting his hands dirty as a favor. First he verifies there is low oil pressure. So he pulls the valve covers and sees the lifters are weak, but the springs are in good shape and a leakdown shows the intake/exhaust as well as the head gasket are looking good. My mechanic says the top end looks extremely clean and well maintained.

Next step, we lifted the engine, dropped the pan and my mechanic took a peek at the main bearings and rod bearings, he said they all looked very good with minimal wear. Cam and crank also looked good. Pan and screen were clean as I change the oil often.

So at this point the engine runs perfectly, except for the very loud clacking which we are pretty sure is the hydraulic lifters from low oil pressure. Our next and probably final step is to replace the oil pump itself, including the pressure relief spring, but my mechanic is not very optimistic about this. He feels that with the gas that flooded the oil some sludge might have been knocked free and is now blocking an oil passage, but admits this is a guess since he can't see inside the engine.

He thinks I have always had low oil pressure, maybe due to the oil passages, but the gas flooding made it worse. Keep in mind that I have had a faulty oil gauge for a couple of years, I just never got around to fixing it since this was kind of a beater.

Anyone care to input their tech? At this point it seems like the bottom end is strong, and the top end is in good shape as well other than the possible oil passages.

david s poole · #2 11-26-2007, 12:07 PM

has anyone suggested to look at the plastic oil bridges in the top of each head as they tend to leak and not carry oil to the lifters as they are designed to do?

spinedoc · #3 12-13-2007, 09:15 AM

Thanks David, I mentioned this and he said it was the first thing he looked at, but looked impressed that I knew this.

Currently we have very low oil pressure, 5psi, and worn rod bearings. We are replacing all the bearings and hoping for the best.

If not, then I've got a clean 96 with a rebuilt transmission for sale.

david s poole · #4 12-13-2007, 09:47 AM

just as an aside surely gas contamination would dissolve sludge not just move it around. have you tried a new oil pump?

spinedoc · #5 12-13-2007, 09:48 AM

I am very tempted to try a new oil pump, but at $450 I wanted to check everything else first. Is there no way to specifically test the oil pump?

david s poole · #6 12-13-2007, 09:53 AM

logic would tell me if you have run this long with low oil pressure without catastrophic damage that the oil is getting through but with low pressure.if you replace the pump and relief valve and check the rear of the block for any leaks from oil galley i still think you will need to replace the bridges.